Rivais Wesley, Constine Louis, Pacella Matthew, Joyce Neil, Nagey Maimuna, Webster Matthew, Yoon Jihyung, Jung Hyunuk, Tanny Sean, Lemus Olga Maria Dona, Zheng Dandan
Department of Radiation Oncology, University of Rochester Medical Center, Rochester, New York, USA.
Department of Medical Physics, Creighton University, Omaha, Nebraska, USA.
J Appl Clin Med Phys. 2025 Jan;26(1):e14556. doi: 10.1002/acm2.14556. Epub 2024 Nov 4.
To compare the effect of two linacs designs on fetal dose sparing on a pregnant patient, including estimation of the fetal dose, and the effect of a lead apron.
A patient with a high-grade sarcoma located in the right knee/lower thigh was prescribed 51 Gy (1.7 Gy/Fx) with a simultaneous-integrated-boost (SIB) of 60 Gy to a smaller volume, starting in the 26th gestational week. Volumetric modulated radiation therapy (VMAT) plans with 6MV-FFF were developed using identical dosimetric constraints on a Varian Truebeam Edge with HD-MLC and a Varian Halcyon with double-stacked MLC. Based on patient dimension measurements, an anthropomorphic phantom was constructed using a Rando phantom and saline bags in the patient's Vac-Lok bag. Phantom measurements were performed using OSLDs and TLDs placed at three different planes, corresponding to the pubis, the umbilicus, and the fundus based on patient measurements and projected gestational age, to estimate the fetal dose. Three experimental scenarios were measured, each with CBCT-based image guidance for an accurate, reproducible setup: Edge, Halcyon, and Halcyon with a tri-folded lead apron (0.5 mm × 3 = 1.5 mm Pb) over the phantom abdomen.
Plan quality and total MUs are comparable between the Edge and Halcyon plans. The OSLD-measured whole-course dose to the pubis, umbilicus, and fundus were 18.8, 13.1, and 11.7 cGy, respectively, on Halcyon, on average 27.8% lower than Edge. The repeatability within either dosimeter was good, although TLD showed systematically lower doses. Importantly, both dosimetry systems showed a lower measured fetal dose for the Halcyon plan compared with the Edge plan. Adding a tri-folded lead apron over the abdomen did not meaningfully lower the measured dose.
In this case study, Halcyon demonstrated a better sparing of out-of-field fetal dose compared to TrueBeam Edge. It was shown that lead aprons do not provide additional fetal dose sparing.
比较两种直线加速器设计对一名怀孕患者的胎儿剂量保护效果，包括胎儿剂量估计以及铅围裙的影响。
一名位于右膝/大腿下部的高级别肉瘤患者，从妊娠第26周开始接受51 Gy（1.7 Gy/分次）的处方剂量，对较小体积同时进行60 Gy的同步整合加量（SIB）。使用6MV-FFF的容积调强放疗（VMAT）计划在配备HD-MLC的Varian Truebeam Edge和配备双堆叠MLC的Varian Halcyon上制定，采用相同的剂量学约束。根据患者尺寸测量结果，使用兰多人体模型和患者Vac-Lok袋中的盐水袋构建了一个拟人化体模。基于患者测量和预计孕周，在对应耻骨、脐部和宫底的三个不同平面放置OSLD和TLD进行体模测量，以估计胎儿剂量。测量了三种实验场景，每种场景均采用基于CBCT的图像引导以实现准确、可重复的设置：Edge、Halcyon以及在体模腹部上方放置三层折叠铅围裙（0.5 mm×3 = 1.5 mm Pb）的Halcyon。
Edge和Halcyon计划的计划质量和总跳数相当。Halcyon上OSLD测量的耻骨、脐部和宫底的全程剂量分别为18.8、13.1和11.7 cGy，平均比Edge低27.8%。尽管TLD显示的剂量系统性较低，但两种剂量计的重复性都很好。重要的是，与Edge计划相比，两种剂量学系统均显示Halcyon计划测量的胎儿剂量更低。在腹部上方添加三层折叠铅围裙并没有显著降低测量剂量。
在本案例研究中，与TrueBeam Edge相比，Halcyon在减少野外胎儿剂量方面表现更好。结果表明铅围裙并不能额外减少胎儿剂量。
